Apparatus increasing diode switching speeds

Abstract

An improved current pump for use in a Type II phase-locked loop including diodes employed as on-off switches for completing paths for a source current. Apparatus is disclosed for increasing the switching speeds of the diodes by ensuring that diode bias voltages undergo the smallest possible shifts required to switch the diodes.

What is claimed is: 
     
       1. Apparatus for increasing the switching speeds of a pair of diodes, the pair of diodes consisting of a first diode and a second diode, each having an anode and a cathode, and each diode having a junction voltage being the voltage by which its anode is more positive than its cathode when it is in an ON state, the junction voltage of the first diode being substantially equal to the junction voltage of the second diode;   the apparatus being responsive to first and second voltages, the first voltage having a value of plus one-half the junction voltage when the first diode is to be turned ON and the second diode is to be turned OFF;   minus one-half the junction voltage when the first diode is to be turned OFF and the second diode is to be turned ON; or   zero volts when both the first and second diodes are to be turned OFF,     and the second voltage having a value of plus one-half the junction voltage when the second diode is to be turned ON and the first diode is to be turned OFF;   minus one-half the junction voltage when the second diode is to be turned OFF and the first diode is to be turned ON; or   zero volts when both the first and second diodes are to be turned OFF,     the apparatus comprising a differential buffer circuit having a first input connected to the cathode of the first diode, the voltage at said cathode being a third voltage;   a second input connected to the cathode of the second diode, the voltage at said cathode being a fourth voltage;   a first output operatively derived from the first input being a fifth voltage which is greater than the third voltage by one-half the junction voltage; and   a second output operatively derived from the second input being a sixth voltage which is greater than the fourth voltage by one-half the junction voltage;     a first summer for adding the first voltage and the fifth voltage to produce a first sum, and for applying the first sum to the anode of the first diode; and   a second summer for adding the second voltage and the sixth voltage to produce a second sum, and for applying the second sum to the anode of the second diode.     
     
     
       2. Apparatus for increasing the switching speeds of a pair of diodes, the pair of diodes consisting of a first diode and a second diode, each having an anode and a cathode, and each diode having a junction voltage being the voltage by which its anode is more positive than its cathode when it is in an ON state, the junction voltage of the first diode being substantially equal to the junction voltage of the second diode;   the apparatus being responsive to first and second signals, each being a binary signal having a true state and a false state, so as to switch the first diode ON and the second diode OFF when the first signal is true and the second signal is false;   to switch the second diode ON and the first diode OFF when the second signal is true and the first signal is false;   to switch both the first and second diodes OFF when the first signal and the second signal are both false; and   to switch both the first and second diodes OFF when the first signal and the second signal are both true,     the apparatus comprising: a first circuit responsive to the first and second signals for producing a first voltage having a value of plus one-half the junction voltage when the first signal is true and the second signal false;   minus one-half the junction voltage when the second signal is true and the first signal false; or   zero volts when the the first and second signals are both true or both false,     a second circuit responsive to the first and second signals for producing a second voltage having a value of plus one-half the junction voltage when the second signal is true and the first signal false;   minus one-half the junction voltage when the first signal is true and second signal false; or   zero volts when the first and second signals are both true or both false,     a third circuit having a first input connected to the cathode of the first diode, the voltage at said cathode being a third voltage;   a second input connected to the cathode of the second diode, the voltage at said cathode being a fourth voltage;   a first output operatively derived from the first input being a fifth voltage which is greater than the third voltage by one-half the junction voltage; and   a second output operatively derived from the second input being a sixth voltage which is greater than the fourth voltage by one-half the junction voltage;     a first summer for adding the first voltage and the fifth voltage to produce a first sum, and for applying the first sum to the anode of the first diode; and   a second summer for adding the second voltage and the sixth voltage to produce a second sum, and for applying the second sum to the anode of the second diode.     
     
     
       3. The apparatus recited in claim 2 wherein the third circuit establishes a common-mode voltage for the third and fourth voltages, the common-mode voltage being substantially constant and being substantially equal to the average of the third voltage and the fourth voltage.